Marine commanders in Iraq are investigating an incident in which a Marine apparently shot and killed a severely wounded and unarmed Iraqi in a mosque in Fallujah, a Pentagon official said last night.

Images of the incident, captured Saturday on videotape by Kevin Sites, a freelance correspondent working for NBC News who is embedded with a Marine unit, were broadcast last night on several news networks. The videotape shows a squad of Marines entering the building and seeing several Iraqis lying against a wall, either dead or gravely wounded. One Marine shouts something about one Iraqi feigning death. The Marine then shoots the man in the head.

The networks did not broadcast the entire tape, saying some of it was too graphic. "NBC has chosen not to air the most gruesome of the images," NBC anchorman Brian Williams said in introducing the videotape.

According to Sites, the wounded men were insurgents who had battled a different group of Marines the day before. In that firefight, 10 Iraqi fighters were killed and five were wounded. Those five were treated with field bandages and left in the mosque because the conditions of combat did not allow the Marines to bring them out. Other Marines were supposed to collect the wounded Iraqis and take them for treatment, but, for reasons not yet known, that did not happen, Sites said.

Then, on Saturday, the Marines received a report that the area, which they thought had been cleared, had been reoccupied by insurgents, Sites said. A different squad of Marines that had not been involved in the previous day's encounter was sent to investigate. It entered the mosque and saw the men lying on the floor. It was then that the shooting occurred, according to the videotape.

The Marine who shot the wounded Iraqi had been wounded the day before but returned to duty. Since the incident he has been taken out of front-line duty, Sites said.

"My understanding is that the Marines have launched an inquiry into it," Pentagon spokesman Bryan Whitman said. He warned against overreacting to the videotape: "I wouldn't jump to any conclusions. We don't know all the facts here."

The Marine investigation was begun yesterday by the staff of the 1st Marine Expeditionary Force, of which the major ground unit is the 1st Marine Division, Whitman said. He said he did not know the unit involved, but Sites is embedded with the 3rd Battalion of the 1st Regiment of the 1st Marine Division, according to his Web site, www.kevinsites.net.

Lt. Gen. John F. Sattler, commander of the 1st Marine Expeditionary Force, in Fallujah, confirmed that an investigation was underway and added: Let me make it perfectly clear: We follow the law of armed conflict. We hold ourselves to a high standard of accountability. The facts of this case will be thoroughly pursued."

Thomas Lee, a former Navy officer who now teaches at Fordham University School of Law in New York, said that since 1864, the Geneva Conventions governing the law of war have prohibited the killing of wounded or sick enemy combatants.

The situation in the videotape appears to resemble an incident in Kufa, south of Baghdad, in the spring that resulted in the Army bringing charges of murder and dereliction of duty against an officer in the 1st Armored Division.

In that May 21 incident, Capt. Rogelio M. Maynulet shot the wounded driver for militant Shiite leader Moqtada Sadr. Maynulet then told a fellow officer that the man was so badly wounded, with part of his skull blown away, that he shot him out of compassion, according to a military legal proceeding held in Germany in September.

Several other Army soldiers in Iraq have been charged with murder, manslaughter and other offenses in connection with the treatment of detainees or curfew breakers. Also, four soldiers in the 1st Cavalry Division have been charged with premeditated murder of Iraqi civilians.

Retired Army Col. Andrew Bacevich said that such incidents can only damage the U.S. cause in Iraq. "We cannot prevail in this conflict if our actions suggest that we do not value Muslim life or that we view Muslims as an inferior species," said Bacevich, who now teaches international relations at Boston University. "My sense is that such an impression has already taken hold in the Arab world. This incident can only reinforce that impression."

Correspondent Jackie Spinner in Fallujah contributed to this report.